Before the advent of coronary artery bypass surgery (CABG), surgical procedures included dissecting the distal end of a left internal thoracic artery from the sternum and chest wall and using the LITA as a conduit to tunnel into the heart muscle to replenish blood supply secondary to coronary artery blockage in the vessel serving that particular area of myocardium. Long term follow-up demonstrated patency of this conduit, although it improved blood supply to only a very small area of myocardium. This procedure then evolved to another method wherein conduits or grafts, i.e. veins from the legs, are attached surgically from the aorta to native coronary arteries in order to direct blood flow past a more upstream local obstruction and into the native coronary artery. The initial use of the LITA revascularization graft was in 1967, and since that time it has been proven that this graft has the highest patency rate in comparison to vein bypass grafts from the legs.
Angiographic assessment of the left internal thoracic artery is important for many reasons, and particularly important in four clinical settings. First, assessment should be performed prior to the insertion of a device to remove arterial obstruction in the proximal left anterior descending coronary artery. Such assessment should also be performed prior to coronary artery bypass graft surgery involving potential bypass to the left coronary system, i.e., left anterior descending coronary artery, diagonal coronary artery, or circumflex coronary artery. Additionally, angiographic assessment is recommended following coronary artery bypass graft surgery where the LITA was used as a bypass conduit. The fourth setting is when a procedure such as percutaneous transluminal coronary angioplasty of the LITA or LITA-anastomosis or distal area in the vessel beyond the LITA insertion is performed.
Atherosclerotic blockage or stenosis of the very proximal left anterior descending coronary artery may be successfully relieved using the catheter balloon technique of percutaneous transluminal coronary angioplasty (PTCA). During this technique, a guiding catheter is placed in the origin of the left main coronary artery and a wire is placed across the left anterior descending coronary artery stenosis followed by a balloon dilatation catheter in the area of stenosis. However, the proximal location of the left anterior descending coronary artery stenosis carries a much lower success rate than PTCA in any other area of this vessel or any other vessel. Indeed, three-month re-stenosis rates may exceed 50 percent in the proximal left anterior descending coronary artery, in contrast to the middle or distal left anterior descending coronary artery or other coronary vessel where the re-stenosis rate at three months is in the 5 to 8 percent range. Moreover, when rapid acute closure occurs, coronary artery bypass surgery mortality rates exceed those performed in a routine scheduled setting. For these reasons, it has been advocated in proximal left anterior descending coronary artery stenosis that the patient should be offered coronary artery bypass surgery as an alternative.
To help with the decision making process, each patient considered for proximal left anterior descending coronary artery PTCA should have pre-PTCA LITA angiography. This permits assessment of the LITA diameter in comparison with the recipient left anterior descending coronary artery (hereinafter referred to interchangeably as LAD). If the diameters or lumens of the LITA and LAD are perfectly matched, then the patient may be encouraged to choose elective low risk coronary artery bypass surgery as opposed to PTCA of the proximal LAD. However, recognizing a much lower long term patency rate for saphenous vein bypass grafts, if the LITA-LAD diameters are mismatched and a saphenous vein (hereinafter referred to as SVBG) is likely to be the conduit, PTCA may be the preferable procedure for proximal left anterior descending coronary artery stenosis.
Most patients undergoing coronary artery bypass surgery have left coronary system atherosclerosis present in one or all of the left anterior descending (LAD), left ventricular diagonal (branch of the LAD), or the circumflex (CIRC) arteries. Therefore, most patients having this surgery will have a LITA bypass if possible. Pre-surgery left internal thoracic artery arteriography should be performed. Such a procedure will provide an assessment of the patency of the left subclavian artery. The LITA arises from the left subclavian artery and any significant atherosclerosis will compromise the flow to the LITA and eliminate it as an acceptable bypass conduit. Additionally, the diameter of the LITA will be identified in order to compare it with native blocked coronary arteries and decide which vessel(s) would be best suited for the bypass graft. The length of the LITA is also determined by use of arteriography to see which stenosed arteries can be reached with the LITA. If a long LITA has a large distal diameter, the graft may be anastomosed so that the side of the LITA inserts into a side blocked coronary artery (side-to-side anastomosis) and the end of the LITA is inserted into the side of another blocked coronary artery (end-to-side anastomosis).
Side branch visualization of the LITA will permit the surgeon and cardiologist to evaluate pre-operatively the appropriate take down or repositioning of the LITA pedicle. If a very large transverse artery side branch is present, a coronary steal syndrome may result whereby blood flow preferentially goes down the transverse vessel to the neck and shoulder muscles (increased with arm and shoulder exercises), instead of down the LITA to the bypassed coronary artery. The large side branch can be ligated if it is in a position that is surgically accessible. In a significant number of cases, a LITA may be rejected as a surgical conduit if the side branches cannot be ligated, for example, if it lies under the clavicle.
If no significant side branches are present proximally, the dissection to free up the LITA pedicle can be limited to just the distal portion of the pedicle. Limiting surgical manipulation is important since excess manipulation may result in external vascular irritation, foreign body giant cell reaction, or late LITA occlusion. Alternatively, a large distal side branch may be found permitting it to be used as a separate conduit, i.e., the LITA would end in two equal sized branches, each of which could be used as a separate bypass graft.
Atherosclerosis infrequently develops in the left internal thoracic artery, but surgical manipulation of the LITA during coronary artery bypass surgery may lead to external factors causing stenosis or occlusion in the proximal portion of the fragile LITA. Although the site of the post surgical total occlusion of the LITA is, accordingly, in the proximal one-third of the conduit, partial stenosis of the LITA graft is usually at the point where the LITA is surgically attached to the native coronary artery. PTCA of a stenotic LITA, anastomosis, or a more distant native vessel has become a successful therapeutic modality for restoring vascular supply to a grafted coronary artery and avoids repeat bypass surgery.
During the conventional PTCA technique, under local anesthesia in the groin (or brachial area), a 7, 8, or 9 French guiding catheter is inserted percutaneously into either the femoral or brachial artery and advanced over a guidewire into the left subclavian and on into the LITA. The large caliber wire is then removed and a small caliber PTCA wire is inserted through the guiding catheter into the LITA and across the stenosis. A balloon catheter (or other device for removing arterial obstruction) is advanced over the PTCA wire into the area of stenosis and is inflated thus restoring normal blood flow to the area of the heart muscle served by the blocked coronary artery.
The large population of patients undergoing coronary artery bypass graft for left coronary artery system disease requiring LITA grafts, the assessment of LITA for PTCA to the proximal left anterior, and the large number of patients returning for repeat coronary artery bypass surgery, (i.e., one-third of the procedures are in patients whose grafts have closed) necessitate LITA angiography in many patients presently undergoing coronary artery catheterization.
However, certain geriatric and congential factors play a role in deterring selective catheterization and angiography of the left internal thoracic artery. In a younger adult the left subclavian arises at a gentle angle from the aorta and is easily entered with a guide wire without manipulation. As the abdominal aorta, lower thoracic aorta and aortic arch elongate with age, they eventually displace the left subclavian superiorly, anteriorly, and toward the right thorax. Initially this produces an "S" shaped subclavian artery which ultimately results in a severe acute angulation of the left subclavian artery from the aorta. This process alone makes selective catheterization of the left subclavian artery very difficult. Displacement of the left subclavian artery is a common finding in older patients returning for catheterization eight to ten years after coronary artery bypass surgery. So, any new device or method of catheterization must take into account the anatomic aging subclavian artery displacement factor.
Considerable congenital variation in the origin of the LITA from the left subclavian artery is also noted. Approximately eighty percent of the LITAs arise anteriorly and inferiorly from the left subclavian artery. In this location the origin may be separate or as a common origin with a transverse vessel. Approximately twenty percent of the LITAs arise anteriorly and superiorly, not from the left subclavian, but from the left thyrocervical trunk artery. Also, the LITA may arise variously from 1 to 4 centimeters from the ostium of the left subclavian artery.
During selective catheterization of the LITA, a dissection or tear in the inside lining of the vessel of the subclavian of LITA may occur due to the fragile nature of the vessel. Dissection of the LITA as a graft has resulted in anterior myocardial infarctions.
Recognizing the inherent congenital and geriatric anatomical technical problems with the femoral approach to the LITA, a brachial approach alternative has been suggested in which an ipsolateral brachial insertion of a guiding catheter for LITA angiography was performed. However, this was associated with complications. Three of eight procedures were complicated by ventricular fibrillation, cardiac arrest, LITA spasm, or dissection.
A special left internal thoracic artery catheter to be used by the right brachial approach has been suggested in a prior art publication, but the technique has not received acceptance due to risk to the right cerebrovascular arteries, and physician unfamiliarity with PTCA via the brachial approach.
Using commercially available performed right Judkins coronary catheters, (or slightly more angular distal tip catheters), entry into a LITA from the femoral artery is inconsistently achieved yet may be associated with vessel trauma. Indeed, as the population of patients requiring LITA selective catheterization angiography gets older, the geriatric technical factors will further reduce successful instances of cannulation of this vessel.
A venous injection of contrast with computer digital subtraction angiography of the LITA has also been suggested. The method was proposed because of technical difficulties of catheterization of the LITA, and to improve visualization in patients with subclavian tortuosity or anomalous LITA origins. The digital subtraction angiography method was subsequently extended to an invasive procedure. After a cardiac catheterization the patient is taken to the X-ray department where an aortic injection of contrast was provided followed by digital subtraction angiography. However, poor visualization of the distal LITA and absence of visualization of the bypassed native arteries make the procedure not only an impractical one, but one which fails to meet the criteria established for adequate visualization of the LITA. Also, without selective catheterization, PTCA could not be performed through this technique.
U.S. Pat. No. 4,909,258 suggested use of a catheter with a distal balloon and proximal port similar to that used years ago for dry limb angiography. The procedure involved occluding blood flow to the distal subclavian ancillary artery, identifying the LITA, and then entering the LITA through the side port with a guidewire and apparatus to remove vascular obstruction. The disclosed apparatus will not find usefulness to solve the current problems for several reasons. First, the apparatus will not be able to properly enter the displaced left subclavian. Most of the patients returning for repeat angiography after LITA graft surgery are in the older age group where geriatric changes in the subclavian have already started to occur. Second, the technique requires inflation of a balloon in an otherwise normal subclavian artery just distal to the LITA. It is well known that balloon inflation in a normal artery is considered traumatic. With wire and PTCA manipulation, the balloon may, in itself, produce shear forces sufficient to expose subendothelial tissue and cause thrombogenic trauma leading to the release of tissue factors resulting in stenosis of the vessel. Furthermore, the system described will not offer sufficient support and pushability or ease of advancement of an apparatus over the wire to remove vascular stenosis. An example of this problem occurs when the apparatus is advanced through the balloon catheter over the wire and into an accordionized LITA or area of stenosis, resulting in the entire apparatus prolapsing retrograde proximally into the subclavian.
Accordingly, a safe and reliable method and apparatus to enter the left subclavian artery and successfully cannulate the LITA is needed to provide complete pre-operative, pre-proximal LAD PTCA, and post-coronary artery bypass surgery angiography and angioplasty for either a normal or displaced left subclavian artery. It has been discovered that the normal or displaced left subclavian artery and variably positioned LITA can be consistently, safely, and selectively catheterized using the apparatus and method of this invention.
Another object of the present invention is to selectively simultaneously visualize the left subclavian and LITA artery/graft and its native/bypassed blocked coronary artery without traumatizing the vessels.
Yet another object of the present invention is to provide a strong platform support in order to remove a stenosis in the LITA artery/graft or its bypassed native vessel without catheter manipulation and with continuous blood flow to the heart muscle/myocardium through the side hole and end hole combination of the device of the present invention.
Accordingly, this invention is an apparatus and direct method for simultaneously injecting radiopaque media or contrast into a left subclavian, LITA artery/graft or its bypassed vessels. Preferred catheter characteristics include a soft, deformable short tip; a canted, distal curve on the catheter tip to hook or engage the left subclavian artery; and a series of primary curves to accommodate the varying LITA-subclavian artery combinations, with side ports in the primary curves, and a firm shaft with pushability into the primary curves.
This apparatus is preferably percutaneously inseted into the femoral artery over a guidewire and advanced to the ascending aorta and then into the left subclavian and left internal thoracic artery. Radiopaque media is then injected and exits through the side ports to the left subclavian and through the distal tip port to visualize a LITA artery/graft, its branches, and bypassed coronary arteries.
The present invention is also an apparatus and method for enlarging the LITA/graft, its anastomosis, or the native vessels served by the LITA/graft. A guidewire is directed past the side ports and exits through a distal port into the LITA/graft and into a native bypassed vessel. A continuous supply of blood flows through the left subclavian artery, into the side holes, down the catheter lumen and into the LITA graft, permitting continuous profusion of myocardium in the distribution of the bypassed vessel. An apparatus to remove arterial blockage is then advanced over the guidewire in the area of obstruction (balloon catheter, atherectomy device, laser catheter, stints, impregnable chemicals, or other means). It is, therefore, yet another object of this invention and apparatus to selectively cannulate the LITA in order to provide an apparatus to remove arterial obstruction while perfusing the distal vessel continuously with fresh oxygenated blood.
Objects and advantages of the present invention in achieving these and other goals will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein are set forth by way of illustration and example certain embodiments of the present invention.